Do you think GT4 will ever be possible to backup you think?

Is this game a DVD9 by the way? Is it the only ps2 that is a DVD9 game? are there any others? Even if it were possible to back it would need a DVD D layer disc to burn it too would it not? hence it would need also a dvd burner that can burn D layer also?

No, there are several other DVD9 games for PS2 such as Metal Gear Solid 2: Substance and Xenosaga.

There are already numerous ways to burn PS2 DVD9 games. I'm not sure if you can reduce the quality to fit it on a single DVD5 or not (I don't think you can) but you can burn it to a DVD-DL or two DVD5s.